NASA Begins Testing of New Spectrograph on Agency's Airborne Observatory

Astronomers are eagerly waiting to begin use of a new instrument to study
celestial objects: a high-resolution, mid-infrared spectrograph mounted on
NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA), the world's
largest flying telescope.

This new instrument, the Echelon-Cross-Echelle Spectrograph (EXES), can
separate wavelengths of light to a precision of one part in 100,000. At the
core of EXES is an approximately 3-foot (1 meter) bar of aluminum called an
echelon grating, carefully machined to act as 130 separate mirrors that split
light from the telescope into an infrared "rainbow."

SOFIA is a heavily modified Boeing 747 Special Performance jetliner that
carries a telescope with an effective diameter of about 8-feet (2.5-meters)
at altitudes of 39,000 to 45,000 feet (12 to 14 km), above more than 99
percent of Earth's atmospheric water vapor. Lower in the atmosphere, at
altitudes associated with most ground-based observatories, water vapor
obscures much of what can be learned when viewed in the infrared spectrum.

"The combination of EXES's high spectral resolution and SOFIA's access to
infrared radiation from space provides an unprecedented ability to study
celestial objects at wavelengths unavailable from ground-based telescopes,"
said Pamela Marcum, a program scientist at the SOFIA Science Center and
Program Office in Moffett Field, California. "EXES on SOFIA will provide data
that cannot be obtained by any other astronomical facility on the ground or
in space, including all past, present or those observatories now under
development."

EXES successfully carried out its first two flights on SOFIA on the nights of
April 7 and 9, according to Matthew Richter, leader of the team that is
developing the instrument at the University of California, Davis, Physics
Department. EXES is a collaboration between U.C. Davis and NASA's Ames
Research Center in Moffett Field.

"During the two flights, EXES made observations to investigate and
characterize the instrument's performance. All the main goals of these
observations were successful, although further commissioning flights are
required to test EXES in all of its modes," said Richter.

On the first commissioning flight, EXES observed emissions from Jupiter's
atmosphere in two molecular hydrogen lines. These observations will be used
to understand how gas rises from deep in Jupiter's interior and mixes into
the planet's upper atmosphere.

During the second commissioning flight, EXES observed a young, massive star
in the constellation Cygnus that is still embedded in its natal cocoon. The
star, known as AFGL 2591, warms up the surrounding interstellar dust and
causes ice coatings on the dust to evaporate. The warmed dust provides an
excellent background infrared "lamp" to probe the chemical make-up of the
intervening gas.

New stars and planets are forming from that material through processes
similar to the ones that made the sun and Earth. These observations are
designed to study water vapor around the protostar, and demonstrate that EXES
can detect absorption from the lowest energy level of water molecules despite
interference from water vapor from Earth's atmosphere.

"Of the observations obtained during the instrument's first flights, only one
can be done from the ground, albeit with some difficulty, and the others are
impossible from even the best ground-based telescope sites because the water
in Earth's atmosphere is opaque at these wavelengths," Richter said. "While
space observatories are above Earth's atmosphere, the massive optical
equipment required to separate the light as finely as EXES does ??? EXES
weighs almost 1,000 pounds ??? would be a challenge to launch into space. In
these observations, the spectral features we are studying are narrow, and
finely dividing the infrared spectrum to detect them is exactly what EXES was
designed to do."

SOFIA is a joint project of NASA and the German Aerospace Center (DLR). The
aircraft is based at and the program is managed from NASA Armstrong Flight
Research Center's facility in Palmdale, California. NASA's Ames Research
Center, manages the SOFIA science and mission operations in cooperation with
the Universities Space Research Association (USRA) headquartered in Columbia,
Maryland, and the German SOFIA Institute (DSI) at the University of
Stuttgart.